DTMF Origins - The Fortuitous Mistake

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DTMF

DTMF was designed to provide address signaling to CO in PSTN at start of call
Speed user address input (rotary dial was slow)
DTMF originally turned off during conversation part of call
Left on during call because of tip-ring polarity administration issues

DTMF Origins

Created simple, universal user input mechanism for all devices on the PSTN network
end-to-end signaling
standard across all PSTN terminal devices
uPSTN service and application vendors discovered DTMF availability during call in late 70s & began using DTMF for application control

DTMF Usage Today

Virtually all PSTN terminals today have a standard 12-key keypad as a minimum
DTMF for Address signaling is ubiquitous
Universal User Input mechanism - DTMF has become the standard user input mechanism for all types of PSTN voice terminals to interact with services and applications

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